The present invention relates to active hydraulic anti-vibration supports and to active anti-vibration systems incorporating such supports.
More specifically, the invention relates to an active hydraulic anti-vibration support designed to be inserted between two rigid elements in a motor vehicle in order to damp and filter vibrations between these two elements, this support comprising at least:
first and second rigid frames which can be joined to the first and second rigid elements respectively,
an elastomer wall linking the first and second frames to one another and defining a working chamber filled with liquid,
a piston which has at least one face in contact with the liquid and which is mounted on the first frame so that it can be displaced in an axis of vibration, this piston being biased towards a rest position by resilient means,
an electromagnetic actuator comprising:
an electromagnet comprising an electric coil co-operating with a metal frame,
a mobile magnetic core which is displaceable under the action of the electromagnet and which is linked to the piston in order to generate counter-vibrations in the liquid.
An active anti-vibration support of this type is described in document EP-A-0 893 620, for example, which discloses a variant having an electromagnetic actuator with a single electromagnet co-operating with a return spring.
These known active anti-vibration supports have position sensors for the piston and their chain of command includes a system automatically controlling this position, allowing the electromagnetic actuator to operate over a very broad range of frequencies, including whilst the vehicle is travelling.
Anti-vibration supports of this type are satisfactory as far as their anti-vibration effect is concerned but have the disadvantage of being complex and expensive and require control means which are in turn complex and expensive.
In an attempt to overcome this disadvantage, various pneumatically controlled active anti-vibration supports have been proposed, such as that disclosed in document JP-A-9 317 815. In practice, these pneumatically controlled supports generally use a vacuum source which is also used to assist braking.
For reasons of safety, however, certain automotive manufacturers do not wish to use the vacuum source of the assisted braking system to control the active supports. Furthermore, pneumatically controlled active anti-vibration supports are still relatively costly and complex insofar as these supports require a connection to the vacuum source. Finally, not all motor vehicles allow a link to a vacuum source.
Accordingly, the objective of the present invention is to overcome the above-mentioned disadvantages inherent in electromagnetically controlled active anti-vibration supports, without having to resort to a pneumatic control system.
To this end, the invention proposes a hydraulic anti-vibration support of the type in question which is essentially characterised in that the electromagnetic ac-actuator, the shape of the frame of the electromagnet and the mobile core being designed so that when an electric current of a value within a normal operating range is passed through the coil and the mobile core is located within a certain range of positions corresponding to the normal operating range of the electromagnetic actuator, the mobile core is subjected to a force which depends solely on this current (in particular, the electromagnetic actuator may be a proportional solenoid, known per se in other applications, which exerts a force proportional to the current passing through the coil or to the square of this current: examples of solenoids of this type are described in particular in documents EP-A-0 785 558, EP-A-0 762 442 and U.S. Pat. No. 4,998,074).
As a result of these features, the electromagnetic actuator of the anti-vibration support proposed by the invention can be controlled in a very simple manner, merely by controlling the electric current passing through the coil of the electromagnet. In practice, since the force exerted by the actuator on the liquid of the anti-vibration support depends solely on said current and not on the position of the mobile core, it is no longer necessary to measure this position or to use a position control system as a means of accurately controlling the force exerted on the piston at each instant.
The control means needed to control the anti-vibration support proposed by the invention are therefore very much simplified and in particular may be provided by the central electronic processing unit of the motor vehicle.
It should be pointed out that the anti-vibration support proposed by the invention offers maximum effectiveness at relatively low frequencies (typically from 20 to 40 Hz in a 4-cylinder internal combustion engine and more generally from 0 to 100 Hz), corresponding to operation of the engine during idling. Since these are the frequencies which create the most unpleasant and most perceptible effects to the vehicle user, the effectiveness of the anti-vibration support proposed by the invention is particularly satisfactory.
When the engine is operating at speeds higher than idling, which normally corresponds to a situation in which the vehicle is driving, a higher current than normal is temporarily circulated in the coil of the electromagnet in order to lock the electromagnetic actuator by causing the mobile core to xe2x80x9cstickxe2x80x9d to the frame of the electromagnet, it then being possible to reduce this locking current once the mobile core has xe2x80x9cstuckxe2x80x9d.
However, the electromagnetic actuator of the anti-vibration device proposed by the invention could continue to operate at higher frequencies than idling in order to continue generating counter-vibrations with a view to cancelling out the engine vibrations.
In preferred embodiments of the anti-vibration support proposed by the invention, one and/or the other of the following features may optionally be incorporated:
the shapes of the frame of the electromagnet and the mobile core are designed so that the mobile core is subjected to a force proportional to the square of the intensity of the electric current passing through the coil when this electric current is of a value falling within the range of positions corresponding to normal operation of the electromagnetic actuator;
the anti-vibration support also has a flexible elastomer wall which is supported by the first frame and defines a compensating chamber filled with liquid communicating with the working chamber via a throttled passage;
the anti-vibration support also has a control chamber filled with liquid, which communicates with the working chamber via a throttled passage, the piston being in contact with the liquid contained in this control chamber;
the force exerted by the electromagnet on the mobile core is always directed in a same direction and has a certain mean value, the resilient means being arranged so as to bias the mobile core in the direction opposite the force exerted by the electromagnet, these resilient means being dimensioned so that when the electromagnetic is exerting said mean force on the mobile core, the mobile core is located in a mean position, substantially centred relative to the range of positions corresponding to normal operation of the electromagnetic actuator;
the frame and the mobile core are made from a laminated metal material and one constitutes a first magnetic element and the other a second magnetic element, the frame being substantially U-shaped with a base extending along a transverse axis perpendicular to the axis of vibration between two side branches extending parallel with the vibration axis, the coil being disposed between the side branches and centred on the vibration axis surrounding a central rod extending along said vibration axis and belonging to the first magnetic element, this central rod being separated from the second magnetic element by a certain air gap along the vibration axis, and the second magnetic element also having two first linearization poles which frame the central rod along the transverse axis and which extend parallel with the vibration axis inside the coil, being of a transverse width which decreases towards the first magnetic element, the two first linearization poles and the central rod respectively having parallel faces facing one another;
the first magnetic element also has two second linearization poles which are reciprocally aligned along the transverse axis and which are arranged outside the coil, these second linearization poles being of a transverse width which decreases towards the second magnetic element, this second magnetic element comprising two axial walls extending along the vibration axis and framing the two second linearization poles, the two second linearization poles and the two axial walls respectively having parallel faces facing one another.
Furthermore, another objective of the invention is to provide an active anti-vibration system incorporating an anti-vibration support as defined above and a control circuit which supplies the coil of the electromagnet, this control circuit being set up so as to determine at each instant the current applied to the coil as a function of at least one parameter linked to engine operation, independently of the instantaneous position of the mobile core relative to the frame of the electromagnet.
In preferred embodiments of the anti-vibration system proposed by the invention, one and/or the other of the following features may be incorporated:
the control circuit has a computer controlling the engine of the motor vehicle which is set up to determine at each instant the electric current applied to the coil of the electromagnet as a function of a synchronisation signal linked to the real operating cycle of the engine and as a function of data stored in memory, said stored data giving at least the amplitude and the phase of a signal representative of the electric current applied to the coil as a function of said synchronisation signal;
the signal representative of the electric current is substantially a rectangular signal and the anti-vibration support has a control chamber filled with liquid which communicates with the working chamber via a throttled passage, the piston being in contact with the liquid contained in this control chamber;
the control circuit is set up so as to apply to the coil of the electromagnet an electric current which is strong enough to lock the mobile core if the synchronisation signal corresponds to a speed in excess of a pre-determined frequency.